An airbag assembly is commonly installed in a vehicle to protect an occupant in the event of a crash or collision. A typical airbag assembly comprises a reaction device, an airbag coupled to the reaction device, and an inflator also coupled to the reaction device. The reaction device is coupled to a structural component of the vehicle. For example, in a passenger-side airbag assembly, the airbag assembly will commonly be incorporated into the dashboard or instrument panel of the vehicle.
The airbag will almost always include a bag which is made of a flexible fabric, such as nylon, and which is designed to be fully inflated to a desired geometry. For example, in a passenger-side airbag assembly, the bag will usually be adapted to inflate to a roughly cylindrical or pillow-like shape. The bag will include portions defining a chamber and a mouth portion defining an inflation fluid inlet which communicates with the chamber.
At the onset of a crash or collision, the inflator supplies inflation fluid to the bag to inflate the airbag towards the occupant. More particularly, the inflation fluid flows through the bag inlet and into the chamber to inflate the airbag. During the inflation process, the kinetic energy of the inflation fluid imposes forces upon the airbag. The airbag is subjected to initial forces during initial stages of the inflation process, intermediate forces during intermediate stages of the inflation process, and final forces during final stages of the inflation process.
An airbag is generally designed so that when it is fully inflated to a final shape, a front or "occupant-contacting" portion of the airbag will contact an occupant situated in the expected position in the associated vehicle seat. In this manner, the in-position occupant is cushioned against impact with a structural part of the vehicle. For a passenger-side airbag, an in-position occupant is situated adjacent the side of the vehicle opposite the steering wheel and his/her torso is located adjacent the back of the passenger seat.
As the occupant contacts the airbag, he/she will be subjected to any forces created during the inflation process which are not absorbed by the airbag. Thus, if an airbag does not adequately absorb such forces, the occupant may be subjected to them. Accordingly, one of applicant's airbag design concerns is the dissipation of these forces prior to the airbag contacting the occupant so that his/her contact will be of a relatively gentle nature.
Another of applicant's airbag design concerns is the protection of an out-of-position occupant. As was indicated above, an airbag is generally designed so that its occupant-contacting portion will contact an occupant situated in the expected position. However, in some instances, an occupant may not be positioned in this manner and may instead be situated towards the center of the seat and closer to the instrument panel.
The present invention provides an airbag inflation-controlling member which controls the shape of an inflatable bag and absorbs forces imposed on the bag during the inflation process. Specifically, the inflation-controlling member causes the bag to assume a shape compatible with protecting an out-of-position occupant during the initial stages of the inflation process. Additionally, the inflation-controlling member dissipates kinetic energy prior to the bag contacting an in-position occupant so that such contact will be of a relatively gentle nature.
More particularly, the present invention provides a vehicle airbag comprising an inflatable bag and an inflation-controlling member which is coupled to the bag. The inflation-controlling member extends through the chamber of the bag during the inflation process and controls the shape of the bag. The inflation-controlling member includes a releasable connection and a stretchable section. The releasable connection remains intact during the initial stages of the inflation process so that the inflation-controlling member extends to an initial length and the bag assumes an initial shape. The releasable connection releases during intermediate stages of the inflation process so that the inflation-controlling member extends to an intermediate length and the bag assumes an intermediate shape. The stretchable section stretches during the final stages of the inflation process so that the inflation-controlling member extends to a final length and the bag assumes a final shape. The initial shape of the bag is designed to protect an out-of-position occupant and the final shape of the bag is designed to protect an in-position occupant.
Preferably, the inflation-controlling member comprises a tether having a first end attached to the bag and a second end also attached to the bag. The releasable connection and the stretchable section are positioned on the tether intermediate the first and second ends. The first end of the tether is attached to the mouth portion of the bag and the second end of the tether is attached to the occupant-contacting portion of the bag.
More preferably, the inflation-controlling member is a three-piece tether comprising a first end piece, a second end piece, and a central piece joining the first end piece to the second end piece. The first and second end pieces include the first and second ends of the tether, respectively. The releasable connection joins intermediate portions of the first and second end pieces together and the central piece comprises the stretchable section of the inflation-controlling member. The releasable connection may be formed with break-away stitching. The stretchable section may be made of a material having a 45.degree. weave pattern.
Thus, the present invention provides a tether-like member for controlling the shape of an inflatable bag and absorbing forces imposed on the bag during an inflation process. When incorporated into an airbag, the tether-like member allows for a three-stage inflation process in which an out-of-position occupant will be protected and an in-position occupant's contact with the bag will be of a relatively gentle nature.
In the past, airbags have been developed which incorporate tether-like members having either a releasable connection or a stretchable section. For example, U.S. Pat. No. 3,879,056 to Kawashima et al. discloses an airbag including a member which is secured to side portions of the bag. The member includes a central folded part having a releasable connection formed by break-away stitching. The releasable connection is designed so that when an occupant contacts the bag, the stitching is broken, the central folded part is released, and the member expands from a first length to a second length. In this manner, the rebounding force of the airbag is absorbed or dissipated.
Additionally, U.S. Pat. No. 4,966,389 to Takada discloses an airbag in which four tether-like members extend between, and are connected to, the mouth portion of the bag and the occupant-contacting portion of the bag. The members are connected to the mouth portion of the bag by a fastener which includes resilient portions composed of 45.degree. bias material. During the latter stages of the inflation process, the members abruptly arrest the movement of the occupant-contacting portion of the bag thereby imposing significant high tensile forces on the members. The resilient portions of the fastener absorb the high tensile forces to prevent separation of the members from the mouth of the bag.
Thus, the prior art discloses tether-like members having either a releasable connection or a stretchable section. However, the prior art members are not believed to allow for a three-stage inflation process in which an out-of-position occupant will be protected and an in-position occupant's contact with the bag will be of a relatively gentle nature. Applicant therefore believes that a need remains, and that present invention satisfies such a need, for an inflation-controlling member which accommodates design criteria associated with both out-of-position and in-position occupants.